In recent years, non-thermal plasma generated in a packed bed reactor has been shown to be effective in reducing nitric oxides (NOx) produced by power plants and standby generators. These units usually have a reducing agent, such as urea, to enhance the conversion efficiency. The packed bed reactor consists essentially of a high voltage center electrode inserted into a cylinder of dielectric material, usually a form of glass or quartz.
An outside or ground electrode is formed by a coating of metal in various forms, including tape, flame spray, mesh, etc. The space between the center electrode and the inside diameter of the dielectric tube is filled with small diameter glass beads. When high voltage alternating current is applied to the center electrode, the surfaces of the beads go into corona, producing a highly reactive and selective surface for inducing the desired reaction in the gas.
Unfortunately, the packed bed design with its loose beads and glass dielectric is impractical for use in the conditions found in a mobile emitter, such as a car or truck. The vibration and wide temperature swings of the vehicle system would damage the packed bed and the necessary temperature and vibration isolation needed to make it survive would not be cost effective.
A reactor for use with diesel engines and other engines operating with lean air fuel mixtures is disclosed in commonly assigned U.S. patent application Ser. No. 09/465,073, now U.S. Pat. No. 6,464,945 entitled “Non-thermal Plasma Exhaust NOx Reactor”, which is hereby incorporated by reference herein in its entirety. Disclosed therein is a reactor element comprising high dielectric, nonporous, high temperature insulating means defining a group of relatively thin stacked cells forming gas passages and separated by the insulating means. Alternate ground and charge carrying electrodes in the insulating means on opposite sides of the cells are disposed close to, but electrically insulated from, the cells by the insulating means. The electrodes may be silver or platinum material coated onto alumina plates and are coated in a pattern that establishes a separation between the electrodes and the connectors of alternate electrodes suitable to prevent voltage leakage. Conductive ink is sandwiched between two thin nonporous alumina plates or other suitable insulating plates to prevent arcing while providing a stable electrode spacing for a uniform electric field.
There remains a need for an improved non-thermal plasma reactor and an improved method of preparing same which lowers overall cost by reducing manufacturing complexity, the number of components and provides design and manufacturing flexibility.